This invention relates to a damper adapted for use in a vehicle suspension system, and more particularly to a vehicle damper providing digressive force versus velocity performance at low damper velocities.
A hydraulic damper used in a vehicle suspension system, such as a shock absorber or a MacPherson strut, must be capable of reacting to and dissipating energy under all types of driving conditions and road obstacles that the vehicle may encounter. The vehicle damper must be capable of handling low velocity inputs, such as chassis sway, encountered during normal maneuvering of the vehicle, and high velocity inputs when the wheels of the vehicle encounter bumps or potholes in the road surface.
In order to accommodate both low and high velocity movements of the suspension, vehicle dampers often include one or more valves having a notched orifice disk, of the type illustrated in FIG. 1. Under low velocity input conditions, the orifice disk is clamped against a valve seat to close off flow apertures within the damper that allow passage of fluid through the internal components of the damper. When a high velocity input to the damper is encountered, fluid in the flow apertures reaches a pressure that is high enough to force all or a portion of the orifice disk off of the valve seat, thereby allowing the internal components of the damper to move through the fluid and provide high velocity damping of the suspension. The orifice disk may be part of a blow-off valve assembly, where the orifice disk is held against the valve seat by a spring, until the pressure in the flow apertures increases to an opening pressure at which force, generated by the fluid pressure in the flow apertures acting against the orifice disk, compresses the spring, and the entire orifice disk lifts off of the valve seat to provide a large effective orifice area for the passage of fluid during dissipation of the high velocity input by the damper. Alternatively, the orifice disk may be part of a deflecting disk valve, where the central portion of the disk remains clamped to the valve seat, and the outer periphery of the orifice disk flexes away from the valve seat to allow passage of fluid during high velocity inputs to the damper, when the fluid pressure in the flow apertures acting on the orifice disk reaches a pressure high enough to cause the disk to deflect.
During low velocity input conditions, the orifice disk remains clamped against the valve seat, and fluid in the flow apertures is allowed to bleed through the notches in the outer periphery of the orifice disk. The low speed performance of the damper can be tuned fairly accurately by judicious selection of the size and number of notches in the orifice disk, and the thickness of the orifice disk.
Valves having notched orifice disks, as described above, provide a fixed area effective orifice during low velocity operation of the damper. Such a fixed area orifice allows fluid to flow through the notches during low speed operation of the damper in such a manner that the force generated by the damper is a generally parabolic function of velocity of the input, as depicted in the low velocity portion xe2x80x98Axe2x80x99 of the operating curve illustrated in FIG. 2. When the opening pressure xe2x80x98Bxe2x80x99 of the valve is reached, the orifice disk blows off or deflects away from the valve seat, thereby increasing the effective orifice area significantly, and the operating characteristic of the damper changes to a linear or much flatter partially parabolic relationship during high velocity operation, as shown by the high velocity portion xe2x80x98Cxe2x80x99 of the operating curve illustrated in FIG. 2.
The parabolic shaped, low velocity operating characteristic provided by valves having fixed area orifice disks is not ideal for all suspension systems, however. In some suspension systems, it is desirable to have a vehicle damper that provides a force versus velocity operating characteristic during low velocity inputs that digresses, as shown in FIG. 3, from the parabolic shape provided by fixed area orifice plates of the type used in prior vehicle dampers, and described above.
What is needed, therefore, is an improved valve assembly and vehicle damper that provides a digressive operating characteristic for damping low velocity inputs to the damper. Preferably, the improved valve assembly can be configured alternatively in the form of a blow-off valve, a clamped deflecting disk valve, or in a valve combining both deflecting disk and blow-off functions. It is also desirable that the improved valve be capable of use in various forms as a compression or a rebound valve on the piston of a vehicle damper, or as a base valve in a dual tube vehicle damper.
Our invention provides such an improved valve and vehicle damper through the use of an imperforate and deflectable, variable orifice disk, having an outer periphery that is only partially clamped against a valve seat, during low velocity operation of the damper, by a variable orifice support disk that has an outer periphery which is not coextensive with the outer periphery of the variable orifice disk. The portion of the outer periphery of the variable orifice disk that is not clamped against the valve seat deflects away from the valve seat during low velocity operation of the damper, in response to force on the variable orifice plate generated by pressure of fluid in flow apertures closed off by the variable orifice plate, to provide a variable orifice for fluid flow through the valve and digressive performance of the damper.
Our invention may take the form of a compression or rebound valve on the piston of a vehicle damper, or a base valve in a dual tube damper. Our invention may take the form of a blow-off valve, a deflecting disk valve, a combination blow-off deflecting disk valve, or as part of other types of valves suited for use in vehicle dampers. A damper according to our invention may include one or more valves according to our invention in combination with other valves of conventional construction.
In one form of our invention, a valve assembly for a vehicle damper includes a valve seat, and orifice disk means. The valve seat defines a flow aperture adapted for receiving a fluid and directing a flow of the fluid through the valve seat. The orifice disk means are adapted for sealing engagement with the valve seat to block the flow of fluid through the flow aperture until the fluid in the flow aperture reaches an opening pressure of the valve, with the orifice disk means providing a variable orifice area for a flow of fluid through the valve prior to the fluid in the flow aperture reaching the opening pressure of the valve. The variable orifice area of the valve allows a flow of fluid through the valve, prior to the fluid in the flow aperture reaching the opening pressure of the valve, that digresses from a parabolic force versus flow characteristic of the type produced by a constant area bleed orifice.
The orifice disk means may include a variable area orifice disk that is partly deflectable away from the valve seat by fluid pressure in the flow aperture acting against the orifice disk when it is in sealing engagement with the valve seat. The deflected disk forms a flow area through the valve that varies in accordance with the pressure of the fluid in the flow apertures prior to the fluid in the flow aperture reaching the opening pressure of the valve.
The flexible orifice disk may have an outer periphery adapted for clamped engagement against the valve seat, and for blocking the flow aperture when the outer periphery of the flexible orifice disk is not deflected away from the valve seat, with the support disk being adapted for clamping less than the entire outer periphery of the flexible orifice against the valve seat. The support disk is shaped for providing only partial clamping and support of the flexible orifice disk against the valve seat, such that fluid pressure within the flow aperture causes localized deflection in a direction away from the valve seat of an unsupported portion of the outer periphery the flexible orifice disk. The deflected unsupported portion of the flexible orifice disk, and a portion of the valve seat adjacent to the deflected portion of the orifice disk, define a bleed orifice having an area for bleed flow through the valve that is variable in accordance with the pressure of the fluid in the flow aperture prior to the fluid in the flow aperture reaching the opening pressure of the valve. The flexible orifice disk may include a non-flexing portion thereof that remains clamped against the valve seat after the opening pressure is achieved.
The valve may also be configured such that the flexible orifice disk lifts away from the valve seat when the operating pressure is reached.
Our invention may also take the form of a vehicle damper including a cylinder tube defining a working chamber for containing a fluid therein and defining an axis. A reciprocating piston slidably disposed in the working chamber includes a first and a second face and a flow aperture extending through the piston from the first to the second face. The vehicle damper includes a piston rod having a first and a second end, with the first end being connected to the piston for linear movement of the rod and piston within the working chamber along the axis, and the second end of the piston rod extending along the axis and out of the working chamber. A valve assembly of the vehicle damper includes a valve seat oriented substantially perpendicularly to the axis and defining a pressure cavity in communication with the flow aperture extending through the piston. A flexible orifice disk of the valve has an outer periphery adapted for clamped engagement against the valve seat, and for blocking the flow aperture when the outer periphery of the flexible orifice disk is not deflected away from the valve seat. A support disk is adapted for clamping less than the entire outer periphery of the flexible orifice against the valve seat. The support disk is shaped for providing support of the flexible orifice disk against the valve seat such that fluid pressure within the pressure cavity causes localized deflection in a direction away from the valve seat of an unsupported portion of the outer periphery the flexible orifice disk. The deflected unsupported portion of the flexible orifice disk, and a portion of the valve seat adjacent to the deflected portion of the orifice disk, define a bleed orifice having an area for bleed flow through the valve that is variable in accordance with the pressure of the fluid in the pressure cavity prior to the fluid in the pressure cavity reaching the opening pressure of the valve.
The variable orifice disk in the vehicle damper may include a non-flexing portion thereof that remains clamped against the valve seat after the opening pressure is achieved. Alternatively, the variable orifice disk may lift away from the valve seat when the operating pressure is reached.
The vehicle damper may include a spring seat adapted for movement along the axis and for clamping the variable orifice disk between the support disk and the valve seat, and a spring for preloading the spring seat, support disk and the variable orifice disk against the valve seat. The spring may be a low rate high preload spring. The spring may have a spring rate in the range of 20 to 60 Newtons per millimeter, and a preload in the range of 100 to 500 Newtons. The spring seat may include a radially extending flange extending generally perpendicularly to the axis and adapted for bearing against the support disk.
The vehicle damper may further include a bushing extending from the valve seat along the axis, the bushing including a guide surface, for guiding the spring seat, support disk and the orifice disk along the axis, and a spring retainer for clamping the spring against the spring seat and the bushing against the valve seat. The guide surface of the bushing may extend past the variable orifice disk when the bushing is clamped between the spring retainer and the valve seat, and the valve seat may include a piloting recess for receiving the portion of the bushing extending past the variable orifice disk when the variable orifice disk is clamped against the valve seat, so that the bushing limits the preload on the spring, and the portion of the bushing extending past the orifice disk, and the piloting recess facilitates assembly of the vehicle damper by precluding the orifice disk from being inadvertently clamped between the bushing and the valve seat.
The portion of the bushing extending past the variable orifice disk may terminate in means for precluding the variable orifice disk from separating from the bushing prior to the bushing contacting the piloting recess in the valve seat. The guide surface of the bushing may be a right circular cylinder concentric with the axis and the means for precluding the variable orifice disk from separating from the bushing may be a radially extending cylindrical pilot, with the piloting recess in the valve seat being configured for receiving and positioning the cylindrical pilot radially and axially with respect to the axis and the valve seat.
In some forms of our invention the valve seat may be formed by a face of the piston in the vehicle damper.
Our invention may be practiced in any form of a vehicle damper that includes a valve having a variable area orifice for low velocity operation of the damper.
Our invention may also take the form of a method for operating a vehicle damper, the method including blocking a flow of fluid through a flow aperture of a valve within the vehicle damper until the fluid in the flow aperture reaches an opening pressure of the valve, and providing a variable orifice area for flow of fluid within the vehicle damper prior to the fluid in the flow aperture reaching the opening pressure of the valve.
A vehicle damper according to our invention may also include a cylinder tube defining a working chamber for containing a fluid therein, a reservoir tube defining a reservoir for supplying fluid to the working chamber, and a base valve assembly. The base valve includes a valve seat separating the working chamber from the reservoir and defining a flow aperture extending through the valve seat for providing fluid communication between the reservoir and the working chamber. The base valve also includes a flexible orifice disk and a support disk. The orifice disk has an outer periphery adapted for clamped engagement against the valve seat, and for blocking the flow aperture when the outer periphery of the flexible orifice disk is not deflected away from the valve seat, and a support disk adapted for clamping less than the entire outer periphery of the flexible orifice against the valve seat. The support disk is shaped for providing support of the flexible orifice disk against the valve seat such that fluid pressure within the flow aperture causes localized deflection in a direction away from the valve seat of an unsupported portion of the outer periphery the flexible orifice disk, with the deflected unsupported portion of the flexible orifice disk, and a portion of the valve seat adjacent to the deflected portion of the orifice disk, defining a bleed orifice having an area for bleed flow through the valve that is variable in accordance with the pressure of the fluid in the flow aperture prior to the fluid in the flow aperture reaching the opening pressure of the valve.
The foregoing and other features and advantages of our invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.